Deviation angle self-compensating substantially achromatic retarder

Abstract

A substantially achromatic multiple element compensator system for use in a wide spectral range, (for example 190-1700 nm), rotating compensator spectroscopic ellipsometer or polarimeter or the like system, which does not require external surface coatings at locations whereat total internal reflections occur. Multiple total internal reflections enter retardance into an entered beam of electromagnetic radiation. Berek-type retarders on both input and output sides of the multiple elements are oriented to minimize changes in the net retardance vs. wavelength via adjustment of Berek-type retarders. Berek-type retarders.

We claim: 
     
       1. A system for introducing a relative phase retardation between orthogonal components of a polarized beam of electromagnetic radiation entered thereinto, said system consisting of at least two sequential elements oriented with respect to one another such that an entered beam of electromagnetic radiation undergoes total internal reflection at least twice in each of the at least two sequential elements; said at least two sequential elements having a sequence, orientation, geometry, and symmetry such that an output beam locus is substantially undeviated and untranslated with respect to an input beam locus, when the system undergoes a translation, or a rotation about said locus of said input beam of electromagnetic radiation, said output beam of electromagnetic radiation being continuous with the input beam of electromagnetic radiation;
 said system being characterized by one selection from the group consisting of:
 there is an external coating at at least one location at which total internal reflection occurs; and 
 there is no external coating at at least one location at which total internal reflection occurs; and 
 
 said system further comprising first and second Berek-type retarders at the input thereto and at the output therefrom, respectively, so that in use a polarized beam of electromagnetic radiation passes through the first Berek-type retarder, undergoes two total internal reflections in the first sequential element, two total internal reflections in the second sequential element, and exits through said second Berek-type retarder. 
 
     
     
       2. A system as in  claim 1 , in which said system does not have any external surface coating at at least one location whereat total internal reflection occurs. 
     
     
       3. A system as in  claim 1 , which comprises at least four sequential elements, and said beam undergoing total internal reflection once in each of the elements, said system being characterized in that each of said at least four elements are right angle prisms having right angle sides adjacent to the right angle thereof and a side opposite the right angle thereof, said right angle prisms being oriented with respect to one another such that, as viewed in side elevation, the first right angle prism is positioned so that it's side opposite the right angle thereof is facing downward and to the right, and so that directly above the first right angle prism is present a second right angle prism, which is oriented so that its opposite the right angle thereof is facing upward and to the left, and so that directly to the right of the second right angle prism is a third right angle prism, which is oriented so that it's side opposite the right angle thereof is facing upward and to the right, and so that directly below said third right angle prism is positioned a fourth right angle prism, oriented so that it's side opposite the right angle thereof is facing downward and to the left;
 said first two right angle prisms encountered by said beam forming, in functional combination, the first of said at least two sequential elements and wherein the reflections in said first two right angle prisms constitute the at least two reflections in said first of said at least two sequential elements, and the second two of said right angle prisms encountered by said beam forming, in functional combination, the second of said at least two sequential elements, and wherein the reflections in said second two right angle prisms constitute the at least two reflections in said second of said at least two sequential elements. 
 
     
     
       4. A system as in  claim 3  in which the angle of the right angle prisms are 45, 90 and 45 degrees. 
     
     
       5. A system as in  claim 3 , in which the right angle prisms are fabricated form fused silica. 
     
     
       6. A system as in  claim 1  which further comprises means for translating and/or tilting at least one of the sequential elements for the purpose of aligning the system such that the output beam is substantially undeviated from said input beam. 
     
     
       7. A system as in  claim 1 , in which there is additionally present a multiple wedge system for use in adjusting relative phase retardation between orthogonal components in a polarized electromagnetic beam, and wherein one said wedge can be rotated with respect to another thereof, and/or both wedges can be rotated simultaneously, for the purpose of aligning the system so that the output beam is substantially undeviated from a locus of said beam input thereinto. 
     
     
       8. A method of applying a system for introducing a relative phase retardation between orthogonal components of a polarized electromagnetic beam entered thereinto comprising;
 a) providing a system for introducing a relative phase retardation between orthogonal components of a polarized beam of electromagnetic radiation entered thereinto, said system consisting of at least two sequential elements oriented with respect to one another such that an entered beam of electromagnetic radiation undergoes total internal reflection at least twice in each of the at least two sequential elements; said at least two sequential elements having a sequence, orientation, geometry, and symmetry such that an output beam locus is substantially undeviated and untranslated with respect to an input beam locus, when the system undergoes a translation or a rotation about Hail said locus of said input beam of electromagnetic radiation, said output beam of electromagnetic radiation being continuous with the input beam of electromagnetic radiation; 
 said system being characterized by one selection from the group consisting of:
 there is an external coating at at least one location at which total internal reflection occurs; and 
 there is no external coating at at least one location at which total internal reflection occurs; and 
 
 said system further comprising first and second Berek-type retarders at the input thereof thereto and at the output therefrom, respectively, so that in use a beam of electromagnetic radiation passes through the first Berek-type retarder, undergoes two total internal reflections in the first sequential element, two total internal reflections in the second sequential element, and then exits through said second Berek-type retarder; 
 said method further comprising: 
 b) causing a polarized input beam of electromagnetic radiation to enter the first Berek-type retarder, then pass through the first and second sequential elements, and pass through the second Berek-type retarder; 
 c) effecting tilt of said first and second Berek-type retarders so that substantially achromatic retardation is entered between orthogonal components of said beam of polarized electromagnetic radiation over a selected wavelength range. 
 
     
     
       9. A method as in  claim 8 , in which the step involving provision of at least two sequential elements comprises providing that each thereof is comprised of two right angle prism elements, in functional combination. 
     
     
       10. A system for introducing a relative phase retardation between orthogonal components of a polarized beam of electromagnetic radiation, said system consisting of at least two sequential elements oriented with respect to one another such that a beam of electromagnetic radiation entered thereinto undergoes total internal reflection at least twice in each thereof;
 said system being characterized by one selection from the group consisting of:
 there is an external coating at at least one location at which total internal reflection occurs; and 
 there is not an external coating at at least one location at which total internal reflection occurs; and 
 
 said system being distinguished and characterized by the presence of first and second Berek-type retarders at the input thereto and at the output therefrom, respectively, so that in use a polarized input beam of electromagnetic radiation passes through the first Berek-type retarder, undergoes at least two total internal reflections in each of the sequential elements, and exits through said second Berek-type retarder as an output beam of electromagnetic radiation, said output beam of electromagnetic radiation being continuous with said input beam of electromagnetic radiation. 
 
     
     
       11. A system as in  claim 10 , wherein the locus of said output beam of electromagnetic radiation is not offset or deviated from the locus of said input beam of electromagnetic radiation. 
     
     
       12. A system as in  claim 10 , in which said system does not have any external surface coating at at least one location whereat total internal reflection occurs. 
     
     
       13. A system as in  claim 10 , which comprises at least four sequential elements, and said beam undergoing total internal reflection once in each of the elements, said system being characterized in that each of said at least four elements are right angle prisms having right angle sides adjacent to the right angle thereof and a side opposite the right angle thereof, said right angle prisms being oriented with respect to one another such that, as viewed in side elevation, the first right angle prism is positioned so that it's side opposite the right angle thereof is facing downward and to the right, and so that directly above the first right angle prism is present a second right angle prism, which is oriented so that its opposite the right angle thereof is facing upward and to the left, and so that directly to the right of the second right angle prism is a third right angle prism, which is oriented so that it's side opposite the right angle thereof is facing upward and to the right, and so that directly below said third right angle prism is positioned a fourth right angle prism, oriented so that it's side opposite the right angle thereof is facing downward and to the left;
 said first two right angle prisms encountered by said beam forming, in functional combination, the first of said at least two sequential elements and wherein the reflections in said first two right angle prisms constitute the at least two reflections in said first of said at least two sequential elements, and the second two of said right angle prisms encountered by said beam forming, in functional combination, the second of said at least two sequential elements, and wherein the reflections in said second two right angle prisms constitute the at least two reflections in said second of said at least two sequential elements. 
 
     
     
       14. A system as in  claim 13  in which the angle of the right angle prisms are 45, 90 and 45 degrees. 
     
     
       15. A system as in  claim 13 , in which the right angle prisms are fabricated form fused silica. 
     
     
       16. A system as in  claim 10  which further comprises means for translating and/or tilting at least one of the sequential elements for the purpose of aligning the system such that the output beam is substantially undeviated from said input beam. 
     
     
       17. A system as in  claim 10 , in which there is additionally present a multiple wedge system for use in adjusting relative phase retardation between orthogonal components in a polarized electromagnetic beam, and wherein one said wedge can be rotated with respect to another thereof, and/or both wedges can be rotated simultaneously, for the purpose of aligning the system so that the output beam is substantially undeviated from a locus of said beam input thereinto.